If you forgot a Windows XP user password, you can log on as an administrator to reset the password. Follow this:
1) Restart the computer.
2) Press CTRL+ALT+DELETE twice, then type the name of the administrator user account.
3) Type the administrator password in the password box, and then click OK.
4) Click START ->> RUN ->> Type ‘control userpasswords2’ ->> click OK.
5) On the Users tab, click the name of the user account that you want to reset the password for, and then click Reset Password.
6) Type a new password in the New password box, and then type the password again in the Confirm new password box, and then click OK.
7) Restart the computer, and then try to log on to Windows again.

If your computer has more than one administrator accounts, then you can log on as some administrator account to reset all other users and administrators password with the same methord.﻿

But if you forgot or lost the only one administrator password, you need to use Windows Password Reset/Recovery Disk to recover the password, or reinstall the system with Boot-CD.